1. Field of the Invention
The present invention relates to a wire bonding system for carrying out wire bonding by means of a wire bonder. More particularly, the present invention relates to the improvement in the operability in a system which is capable of automatic bonding at a plurality of spots irregularly arranged on a substrate.
2. Description of the Related Art
A wire bonder is used, for example, in the process of manufacturing an LED head. The LED head is a light-emitting device used for printing in an LED printer. The LED head has an LED array composed of a plurality of aligned LED chips and has a function of printing any given letter or mark by controlling the intensity of light emitted from each of the LED chips.
FIG. 5 shows an example of the structure of an LED head. In FIG. 5, the LED head is viewed from above a substrate 1 and a part of the substrate 1 and a part of the circuit formed on the substrate 1 are enlarged.
In FIG. 5, the reference numeral 2 represents an LED array. The LED array 2 is composed of a plurality of aligned LED chips, but in FIG. 5, the LED chips constituting the LED array 2 are not shown separately from each other. A plurality of drivers 3 are arranged on the substrate 1. Each driver 3 is an integrated driving circuit and has the function of driving the corresponding LED chip. The wiring between the drivers 3 and the LED chips are omitted for the purpose of simplifying the drawing.
The intensity of light emitted from each LED chip must correspond to a predetermined value. It is therefore necessary that the LED head has the function of controlling the intensity of light emitted from each LED chip to be this predetermined value. This task is assigned to a plurality of current controlling resistors provided within the driver 3. These resistors set a current value which is to be supplied to the LED chip which corresponds to the driver 3. The current value is set at any given value by selecting an appropriate resistor or a combination of resistors.
In the structure shown in FIG. 5, a technique of Au wire bonding is adopted for the selection of a resistor. One end of a current controlling resistor provided within the driver 3 constitutes one terminal of the driver 3 and is electrically connected to a bonding pad 4 through an Au wire 5 by Au wire bonding. All terminals of the driver 3 are first connected to the corresponding bonding pads 4. A resistor is then selected by the selective connection between an appropriate bonding pad 4 and a common electrode 6 through an Au wire 7.
In this way, the current controlling resistors provided in the driver 3 are selectively connected to the common electrode 6. Such selective connection enables the intensity of light emitted from each LED chip to be set at any predetermined value.
In this type of LED head, bonding is carried out for the purpose of controlling the intensity of light emitted from each LED chip. Since the resistors selected are different depending upon the drivers, the bonding pads 4 connected to the common electrode 6 by wire bonding are also different depending upon the driver 3.
A conventional wire bonder is capable of simultaneous bonding to a group of bonding pads in accordance with previously input information on the spots to be bonded. For example, if such a wire bonder is used in manufacturing the LED head shown in FIG. 5, the user of the wire bonder previously sets the bonding pads 4 in one driver 3 which are to be connected to the common electrode 6 as the objects of wire bonding. After the preset bonding pads 4 in the driver 3 are automatically connected to the common electrode 6, the user of the wire bonder must select new bonding pads 4 for the next driver 3 as the objects of bonding before the next wire bonding operation.
Because of this, in manufacturing, for example, an LED head which requires bonding having irregular bonding requirements by means of a conventional wire bonder, much labor is required for selecting and setting the spots to be bonded. This is an obstacle to expeditious operation and inconvenient for the user of the wire bonder.